A(n) is a set of rules that determine what a layer would do and provides a clearly defined set of messages that software at the layer needs to understand.

Protocol is the correct answer of this question.

Explanation:

The protocol is a collection of rules that specify what a level should do, which includes a simple set of notifications that the layer computer requires to understand.A protocol is a basic set of regulations that enable the correspondence between portable devices.

one method is to click on the icon.

only #2 represents an object at rest on a table.

in #1, there is no normal force due to the table; the object is accelerating downward.

in #3, the vertical forces are not balanced; the object is accelerating downward.

in #4, neither the vertical nor the horizontal forces are balanced. the object is accelerating upwards and to the right.